Known level measurement devices increasingly use principles that use the propagation of electromagnetic waves or a reflection behavior and runtime behavior of these waves to determine filling levels. In this case, a high-frequency electromagnetic wave, for example a microwave pulse is emitted by a filling level measuring device in the direction of a surface of a filling material in a container, is reflected by this surface and a filling level is calculated on the basis of the travel-times of the reflected microwave signal.
As a result of further technical developments, in particular of electronics and semiconductor technology, higher frequencies in the upper two-digit gigahertz range are increasingly being used for level measurements. Due to the high frequencies and the resulting physical properties of wave propagation, the requirements for, in particular, the high-frequency components of such level measuring devices are increasing. Frequently, the high frequency assembly is realized on a printed circuit board, which includes the electronics for generating the microwave pulses and the antenna technology.
One possibility of forwarding the generated high-frequency vibrations, for example to an external antenna, exists in the connection of a waveguide. These waveguides can advantageously be used in the frequency range used for forwarding microwave signals. A particular challenge lies in the waveguide transition, i.e., the radiation of the electromagnetic wave from a conductor (for example on the printed circuit board) into the interior of a waveguide and vice versa. This guide may for example be designed as a micro-strip, the end of which extends into a waveguide. The waveguides can be designed, for example, as an air waveguide.
In order to achieve low electrical losses and a good adaptation, in this case, particular technical provisions may be necessary. For example, for low-loss or lossless coupling of the signal, the waveguide must have a resonator at its end whose size, diameter and geometric design minimizes the losses in the range of frequencies used. At the same time, it is desirable to reduce the size of the assemblies and to simplify a structure while maintaining high quality. A technical solution may be to integrate the various functions as possible and to thus obtain simple and inexpensive assemblies. Thus, for example, EP 1 949 491 B1 discloses a waveguide transition in which the resonator of the waveguide is integrated into the printed circuit board.